This invention relates to an apparatus and a method for the prototype and small-batch production of gear wheels.
In the production of gear wheels, prototype or small-batch production recently has increasingly gained importance. When making very expensive and large workpieces, it should rather be prevented that the first workpiece fabricated as prototype must be discarded as reject. In particular the requirement of very short manufacturing times calls for a novel, very flexible and fast manufacturing process.
The previous procedure for the production of prototypes can be divided into the following method steps:    1. First design of the gear teeth regarding the selection of the profile and flank correction, the quality to be chosen, etc.;    2. determining the production process and the finishing method;    3. manufacturing the blank by turning, drilling, etc.;    4. pre-cutting gear teeth for instance by hobbing, shaping, generation grinding or profile grinding;    5. hardening or heat-treating;    6. optionally hard finishing by generation or profile grinding;    7. test operation with the prototype gear wheels on a test stand or in a real transmission; and    8. improved new design or first start of pilot production.
In the aforementioned procedure, upon determining the profile in method step 3, the tool is designed for pre-cutting gear teeth and for hard finishing and is commissioned. The manufacturing and delivery time for these tools is very long and can be up to three months. Possibly desired changes or manufacturing defects on the tool will only become visible during first use thereof, and therefore inevitably lead to the necessary remachining, for instance the decoating, regrinding or recoating of a hob. This involves a loss of production of several days or weeks.
As far as in steps 3 and 6 of the aforementioned method pre-cutting gear teeth and hard finishing should be effected by generation grinding, a galvanically coated dressing tool is required for this generation grinding, which has the special profile shape of the gear teeth. The manufacture of such dressing tool also requires a delivery time of several weeks. As a universally applicable alternative for a profile-adapted dressing tool, a universal dressing tool can also be used, with which the grinding worm is dressed line by line. Here, the special profile shape thus is produced by the control of the grinding or dressing machine. In this method, there is no delivery time for the special tool. However, it is disadvantageous that dressing the grinding worm from the cylindrical blank takes several hours. If corrections in the tooth profile, for instance with regard to the profile angle, tip relief or depth crown, are necessary after generation grinding of the first workpiece, a lengthy line-by-line dressing cycle must be restarted when using a universal dressing tool. Depending on the extent of the correction to be made, such cycle can be very long. In the case of a specially designed profile dresser, however, an even greater production delay is obtained, which can be several weeks, as this dressing tool must be sent back to the tool supplier for correction.
The steps of pre-cutting gear teeth and hard finishing by profile grinding corresponding to method steps 3 and 6 of the aforementioned procedure also can be performed by means of a profile grinding method. When dressing, the inverse profile is applied onto the grinding element and then is transferred onto the workpiece during grinding, wherein a simple kind of movement, such as a very slow linear movement while rotating the grinding element, mostly is sufficient. As compared to the aforementioned generation grinding method, this involves a disadvantage with regard to the machining time, since the profile grinding method is distinctly slower. In particular in the case of great tooth widths and high tooth numbers, distinctly higher grinding times are required. If profile grinding is used for pre-cutting gear teeth, the complete tooth height must be formed. This is referred to as grinding into solid block, in which the machining time again is distinctly longer than in the case of generation grinding.